NZ203505A - U-bolt clamp:upturned ends on keeper - Google Patents

Description

203505 Priority Data(s): ......

Complete Specification Filed: Claas: /r / ot .. i > •»••••■ • ^ 116 AUG 1985 PubKdation Date: P.O. Journal, No: ...... ;/£7r?.....

Patents Form No. 5 PATENT ACT 1953 COMPLETE SPECIFICATION "TREFOIL CABLE CLAMP" WE, GKN AUSTRALIA LTD., a Company incorporated under the laws of the State of New South Wales, Commonwealth of Australia, of Percy Street, Auburn, New South Wales, 2144 Australia, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement 203505 This invention relates to trefoil cable clamps, that is to say clamps intended to surround three electric cables to hold them as a unit in trefoil formation.

Under fault conditions with high currents flowing in the cables the electromagnetic repulsion tending to cause the cables to move away from each other creates high stresses in the clamp and difficulty has been experienced in designing a clamp which is able to counteract those stresses and at the same time is relatively inexpensive and convenient in use.

Those difficulties are enhanced because the clamps cannot be made entirely of steel (because of the need to avoid completely encircling the cables with magnetic material) and because the clamp should preferably be capable of holding the cables firmly together notwithstanding the considerable variation- from their nominal diameters that such cables are likely to exhibit.

An object of the present invention is to provide a clamp which more nearly meets the above indicated desiderata than do prior art clamps.

The invention consists in a trefoil cable clamp, comprising a non-magnetic U-bolt and a keeper spanning the bite of the U-bolt and pierced by two clearance holes through which limbs of the U-bolt respectively extend, characterised in that said keeper has end portions projecting perpendicularly from the remainder of the keeper which lie flat against the outer surfaces of the respective limbs of the U-bolt Thus the keeper ends reinforce the bolt linbs against shearing forces produced in the bolt where it.penetrates the 203505 keeper as a result of applied forces from the cable tending to separate the lirrflps of the U-bolt.

By way of example, a preferred embodiment of the above-described invention is described in more detail hereinafter with reference to the accompanying drawings.

Figure 1 is a front elevation of a trefoil clamp according to the invention with a portion of its keeper cut away.

Figure 2 is a sectional view taken on any one of the 10 lines 2-2 of Figure 1.

Figure 3 is a sectional view taken on either of the lines 3-3 of Figure 1.

Figure 4 is a side elevation of the clamp of Figure 1.

In the illustrated embodiment of the invention a U-bolt 5 is manufactured from- a stainless steel rod which is initially straight and has roll-formed or otherwise threaded end-portions 6.

The U-bolt 5 preferably backs up a U-shaped liner strap 7 which, when the clamp is in use, makes contact with the 20 cables 8, thereby reducing the pressure on the cables 8 by spreading the load from the U-bolt 5 over a bigger area.

That liner strap 7 may be an extruded aluminium alloy strap having two locating ribs 9 on what becomes its outer face in the finished article and between which the U-bolt rod is a neat fit. In manufacture the liner strap is cut to length and the stainless steel rod is laid between the locating ribs with its threaded end-portions projecting beyond the ends of the strap. The assembly is then 203505 press-formed into the required U-shape and, for preference, at least parts 10 of the ribs 9 are crimped over so as to grip the U-bolt 5 tightly. In the finished article the U-bolt has a rounded centre portion 11 flanked by straight, diverging, limbs 12 with an included angle of o approximately 60 , terminating in end-portions 13 which are substantially parallel to each other and which are partly threaded at 6 as aforesaid.

A keeper 14, which may be a mild steel strap extends 10 across the bite of the U-bolt 5. The keeper constitutes the base of a triangle of which the rounded centre portion 10 of the U-bolt 5 constitutes the apex. The parallel end-portions 13 of the U-bolt 5 extend through clearance holes 15 in the keeper 14.

In accordance with the invention, end portions 16 of the keeper 14 outboard of the U-bolt liirfos are extended perpendicularly of the remainder of the keeper in contact with the parallel end-portions 13 of those limbs.

For preference, the clearance holes 15 are elongated 20 holes and after the keeper strap has been shaped an end-portion of each hole 15 extends into a bent up end-portion 16 of the strap. This enables the ends of the U-bolt to make firm contact with the end-portions 16 of the keeper 14 without the need for extreme precision in the manufacturing process.

In use, those portions of the U-bolt limbs extending beond the keeper are furnished with nuts 17 (and preferably washers 18) to enable the clamp to be secured to a suitable JAN 1985 " - 4 - 2035 support structure and to draw the U-bolt towards the keeper to make firm engagement between the cables on the one hand and the U-bolt liner strap and keeper on the other hand.

Claims (6)

WHAT WE CLAIM IS:

1. A trefoil cable clamp comprising a non-magnetic U-bolt and a keeper spanning the bite of the U-bolt and pierced by two clearance holes through which limbs of the U-bolt respectively extend, characterised in that said keeper has end portions projecting perpendicularly from the remainder of the keeper which lie flat against the outer surfaces of the respective limbs of the U-bolt.

2. A clamp according to claim 1 wherein said U-bolt comprises a U-shaped rod having threaded end portions and a liner strap interposed between the inner surface of the rod and the cables to be clamped.

3. A clamp according to claim 2 wherein said liner strap is affixed to said U-shaped rod.

4. A clamp according to claim 3 wherein said liner strap includes two locating ribs projecting from and extending along its outer face between which said rod lies; at least a portion of said ribs being crimped over so as to grip the rod.

5. A clamp according to any one of the preceding claims wherein said clearance holes are elongated and extend at one end into the remainder of the keeper, and at the other end, into the corresponding end portion of the keeper.

6. A trefoil cable clamp substantially as described herein with reference to the accompanying drawings. GKN AUSTRALIA LTD. By Their Authorised Attorneys, JOHN A. REMMINGTON & ASSOCIATES -6-